Jiaming Yuan 80065d571e
[dask] Add DaskXGBRanker (#6576)
* Initial support for distributed LTR using dask.

* Support `qid` in libxgboost.
* Refactor `predict` and `n_features_in_`, `best_[score/iteration/ntree_limit]`
  to avoid duplicated code.
* Define `DaskXGBRanker`.

The dask ranker doesn't support group structure, instead it uses query id and
convert to group ptr internally.
2021-01-08 18:35:09 +08:00
..